An IP address can also be thought of as the equivalent of a street address or a phone number for a computer or other network device on the Internet. Just as each street address and phone number uniquely identifies a building or telephone, an IP address can uniquely identify a specific computer or other network device on a network. An IP address differs from other contact information, however, because the linkage of a users IP address to his/her name is not publicly available information.

You need to know your external internet IP Address from time to time for the following reasons:

To allow users to connect to you with software, where you are acting as a server.

So that associates can establish a V.P.N. connections and map drive letters to your computer or network.

For IP filtering so that only machines from your External IP Address are allowed access.

For establishing links to home computer or server from the internet.

So What is an External IP Address?

An external IP address is the unique identifier assigned to you by your Internet Service Provider (ISP). There are to types of external IP address, static and dynamic. Static is fixed and therefore never changes. Dynamic changes every time you connect to the internet.

Many Internet users, having access through router and running DHCP, experience the same problem - what is the real IP address assigned to them by ISP (Internet Service Provider)? For example, you have a server and you want it to be accessible from outside. So you forward the router port to your local IP and provide the clients with the router external IP address to access the server. If you are lucky, it will work for a long time, if not - your server may become inaccessible the next minute after you set it. The reason: your ISP changed IP address assigned to you. Your router knows it (and dynamically refreshes all the information required for Internet access), your clients dont (and keep hitting the server with an old IP address, wondering why its not responding).

Static And Dynamic Ip address

A Static IP address is where a computer uses the same address every time, as opposed to situations where the user IP address changes frequently, when a user logs on to a network by dialup or on shared residential cable. Static addressing is essential in some infrastructure situations, such as finding the Domain Name Service directory host that will translate names to numbers.

Static addresses are convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a lifetime argument, after which it should be looked up to confirm that it has not changed. Addresses do change as a result of network administration (RFC 2072).

This contrasts with a Dynamic IP address, wherein an IP address is assigned to a computer, usually by a remote server which is acting as a Dynamic Host Configuration Protocol server. IP addresses assigned using DHCP may change depending on the addresses available in the set scope. Dynamic IP Addresses assigned by Dynamic Host Configuration Protocol servers are used because it reduces the administrative burden of assigning static addresses within a network.